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Abstract

Introduction: Thermal characteristics of cryoablation to achieve myocardial conduction block is not well understood. In this study we evaluated the maximum isotherm during cryoablation to achieve conduction block.

Methods: Anesthetized, ventilated canines (n=9) underwent thoracotomy. In in-situ RV outflow tract, blind alley (BA) that conducted to and from the RV only via an isthmus (IS) was created by cut and sew method by making a surgical incision. Cryoablation (7Fr, 8 mm tip FreezorMax3, Medtronic) was performed (4 -6 min per lesion) from the endocardium at the IS. Epicardial temperature was monitored by a thermal camera (FLIR, Danderyd, Sweden). Conduction block was assessed by pacing and recording from inside the BA and from the LV. Acute and chronic block was defined as bidirectional block through the IS at 15 min and 180 min, respectively. Ablation was continued until acute block was achieved and observation continued for 180 min.

Results: Ten preparations were studied. Acute block was achieved in all preparations. IS temperature was ≤ -10C in all samples with chronic block (4/8, p=0.028) and >-10C without chronic block (4/8). Chronic block was not assessed in two due to delay in achieving acute block. Ablation data is summarized in the Table.